Hi Kathy,
I had/have similar symptoms. I was diagnosed with MAC 15 years ago, was on the "Big 3" for 18 months, and have done well since then until last November when the MAC returned. At the same time I found that out, I became ill with a viral/flu-like illness. Shortly thereafter, I started with tingling and weakness in my lower legs, feet, arms,and hands. Like your sister, I had many tests done to determine what was causing it. In the end, it was decided that I had a post viral neuropathy caused by the flu-like illness. The doctor that treats my MAC does not feel that it is/was related to the MAC. My symptoms are better, but have not resolved. We are going to start treating the MAC in a couple of weeks. It will be interesting to see if the neuropathy symptoms go away - I'm not convinced that the two are not related.